1. Field of the Invention
This invention relates to a method for forming an image on an object utilizing a thermal dye transfer system. This invention also relates to a thermal transfer sheet and a thermal transfer image-receiving sheet for use in said method.
2. Background Art
Various thermal transfer recording systems are known in the art, and one of them is a thermal dye transfer system using as a colorant the so-called sublimable dye which is sublimated or diffused upon exposure to heat. In this system, a thermal transfer sheet is used wherein a dye-holding layer comprising a sublimable dye held in a binder resin is provided on one side of a support such as a polyester film. The thermal transfer sheet is prepared by printing or coating, on a heat resisting support, an ink or a coating solution comprising a mixture of a binder resin with a sublimable dye and drying the resultant coating or print.
The thermal transfer sheet is subjected to selective heating from the back side thereof in a printer having heating means, such as a thermal head, to form an image on a thermal transfer image-receiving sheet comprising a substrate sheet and a dye-receptive layer dyable with a dye.
The dye image thus formed, since a dye is used as the colorant, has excellent sharpness and transparency, offering excellent color reproduction and half tone reproduction. By virtue of this nature, the thermal dye transfer system is suitable for the reproduction of a full-color image, wherein many color dots of three or four colors are transferred onto a thermal transfer image-receiving sheet, and can form an image having a high quality comparable to that formed by the conventional offset printing or gravure printing and a full-color photographic image. For the above reasons, the thermal dye transfer system is convenient for easily providing a full-color hard copy of a computer generated or processed image and a video image in a very short time and in fact has been widely used for this purpose.
Due to the structure or mechanism of a printer, however, it is very difficult to form a dye image directly on an object other than a sheet-form object like a thermal transfer image-receiving sheet. This has led to an attempt to produce a dye image using the above thermal transfer sheet on an object having any desired shape other than sheet.
For example, Japanese Patent Laid-Open Nos. 66997/1987 and 203494/1985 propose a method wherein a thermal transfer image-receiving sheet with a dye image formed thereon is attached, like a label, onto an object. This method has the problem that the thermal transfer image-receiving sheet attached on the object, due to the thickness of the sheet, is easy to peel off from the object.
Japanese Patent Laid-Open No. 229292/1992 proposes a method which comprises the steps of peeling a dye-receptive layer, with a dye image formed thereon, from the substrate sheet of a thermal transfer image-receiving sheet, bringing the dye-receptive layer into contact with an object, heating the dye-receptive layer at a high temperature to transfer the dye image to the object, and peeling the dye-receptive layer from the object.
This process requires such a troublesome step that a dye-receptive layer is once peeled off from the substrate sheet of a thermal transfer image-receiving sheet and then pressed against an object. Further, the need for the peeling of a dye-receptive layer imposes a limitation on the selection of materials for both the substrate sheet and the dye-receptive layer. Furthermore, since the peeled dye-receptive layer alone is handled, it should have proper strength and thickness, again imposing a limitation on the selection of materials.
Accordingly, an object of the present invention is to provide a simple method for producing an image on an object which enables a thermal transfer image-receiving sheet, as such, to be used without peeling the dye-receptive layer from the substrate.
Another object of the present invention is to provide a thermal transfer sheet and a thermal transfer image-receiving sheet which, when used in the above method, can achieve good color reproduction without causing a color change and produce a high-density and sharp image on an object.